Study On The Optimal Design Of Ultra-low Specific Speed Francis Turbine

Economic development is often accompanied by energy consumption,and the contradiction between energy supply and demand is gradually prominent.At the same time,there is a large amount of waste of energy in some aspects of social production and life.Under the background that the state proposes to closely focus on industrial energy conservation and green development and implement made in China 2025,research on energy conservation will be carried out.There are tens of thousands of mechanical ventilation cooling towers in China,and the motor driving the fan consumes a lot of electric energy.At the same time,due to the requirements of design,most of the cooling fluid?such as water?in the cooling tower has surplus energy.In the early stage,the research group designed a water turbine to make use of the surplus energy and directly drive the fan to rotate instead of the motor,so as to achieve the purpose of energy saving.Although the turbine can meet the working requirements of cooling tower,its efficiency is relatively low,the loss of water diversion parts is large,the local high pressure phenomenon in the stay vane area is obvious,the negative pressure at the back of the runner is large,and the runner area has the phenomenon of flow separation and vortex.Therefore,the author adopts the idea of orthogonal optimization,aiming at the influence of the geometric parameters of the stay vane and runner on the hydraulic performance of the turbine,carries out the optimization design research.The three-dimensional model is mainly established by Unigraphics NX?UG?software,RNG turbulence model is selected,and computational fluid dynamics?CFD?is used for simulation calculation to predict the performance of hydraulic turbine;the orthogonal scheme is designed with appropriate factors and levels to optimize the parameters,and finally the hydraulic turbine with better hydraulic performance is obtained.The main achievements are as follows:?1?The inlet setting angle,number and outlet angle of the stay vane are studied to find the inlet setting angle more suitable for this type of turbine.By selecting different stay vane number and different inlet setting angle,the matching law of inlet setting angle and number of stay vanes is obtained.By designing a new outlet angle scheme and analyzing the results of each scheme,the outlet angle of the stay vane is determined,so that the hydraulic efficiency of the turbine is higher and the internal flow field of the turbine is better.?2?Selection factors:inlet setting angle,outlet angle,number of blades and upper crown profile,modification of geometric parameters of runner blades,numerical simulation and post-processing of the modified turbine by CFD technology,combined with simulation results,optimization design of flow passage components,analysis of the impact of parameters on the hydraulic performance of the turbine.?3?According to the influence of single factor on the hydraulic performance of the turbine in the previous study,the factors and levels are selected and the appropriate orthogonal table is designed.Nine schemes are drawn up by using four factors and three levels L₉?3⁴?table.Then,according to the scheme,CFX is used for simulation calculation,and CFD-Post is used for post-processing of calculation results to analyze the hydraulic performance of different schemes.?4?Through the range analysis method?R method?,the influence of the level change of each factor on the efficiency of hydraulic turbine is analyzed,and the best parameter combination is put forward.Through the post-processing analysis,the efficiency of the optimized turbine under the rated flow condition is increased by 2.04%,and its internal flow field distribution is better,and its hydraulic performance is greatly improved.?5?On the basis of the above research,the variable flow condition of the turbine is studied.Through regression analysis,the relationship between unit flow and unit speed of turbine is established,and the relationship between unit flow and efficiency is analyzed.The results show that the unit flow rate is 0.1398m³/s and the unit speed is 51.16r/min.At this time,the efficiency is 79.69%,which is 1.43%higher than that of the original water turbine.After optimization,the range of high efficiency zone is increased and the hydraulic performance is better.